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Intel® PXA255 Processor Developer’s Manual 15-15
MultiMediaCard Controller
15.3.2.2 Block Data Read
In a single block data read, a block of data is read from a card. In a multiple block read, the
controller performs multiple single block read data transfers on the MMC bus.
After turning the clock on to start the command sequence, the software must program the DMA to
empty the MMC_RXFIFO (read 32 bytes). The software will continue the process of emptying the
FIFO until all of the data has been read from the FIFO. The software must then wait for the
transmission to complete by waiting for the MMC_I_REG[DATA_TRAN_DONE] interrupt. The
software can then read the status register, MMC_STAT, to verify the status of the transaction.
For multiple block reads, The MultiMediaCard System Specification specifies that the card will
continue to send blocks of data until the stop transmission command is received. After the
controller has received the number of bytes specified in the MMC_NOB register, the controller will
stop receiving data. After the MMC_I_REG[DATA_TRAN_DONE] interrupt is detected, the
software must set up the controller to send the stop transmission command, CMD12. Consult The
MultiMediaCard System Specification for a description of the stop transmission command.
If both receive FIFOs become full during the data transmission, the controller turns the clock off.
Once the software empties the FIFO to which it is connected, the controller turns the clock back on.
In a block data read, the following parameters must be specified:
• The data transfer is a read.
• The block length, if the block length is different from the previous block data transfer or this is
the first time that the parameter is being specified.
• The number of blocks to be transferred.
• The receive data time-out period.
The controller will mark the data transaction as timed out if data is not received before the time-out
period. The delay for the time-out period is defined as:
The software is required to calculate this value and write the appropriate value into the
MMC_RDTO register.
15.3.2.3 Stream Data Write
The stream data write looks like the single block write except a stop transmission command is sent
in parallel with the last six bytes of data.
After turning the clock on to start the command sequence, the software must start the process of
filling the MMC_TXFIFO and starting the clock as describe in Section 15.3.2.1. The software must
then wait for the MMC_I_REG[STOP_CMD] interrupt. This interrupt indicates that the MMC
controller is ready for the stop transmission command. The software must then stop the clock, write
the registers for a stop transmission command, and then start the clock. At this point, the software
must wait for the MMC_I_REG[DATA_TRAN_DONE] and MMC_I_REG[PRG_DONE]
interrupts.
Time-out Delay
MMC_RDTO[READ_TO]()128()×
10
7
------------- ---------------------------------- -------------------------------------------
sec=